The major objective of this research is to study social competence and mastery motivation in the first year of life of infants with Down's syndrome and to examine the relationship between the mother-infant interaction and infant's mastery behaviors. Down's syndrome infants are being studied longitudinally at 3, 6 and 8 months, and a cross-sectional sample is being studied at 12 months of age. Mastery motivation is being assessed using tasks which have been developed in this laboratory. An observational system which preserves the sequence and continuity of the transactions between mother and infant is being employed to examine the mother-infant interaction. In addition, the relationship between the infants' social and mastery behaviors and specific cognitive, and temperamental variables is being examined. Early findings highlight similar performance on cognitive-motivational variables between Down's infants and normal infants. Differences between these two groups in face-to-face interaction have been found.